The present invention relates to hypodermic syringes for administering medication and more particularly to non-reusable or single use, disposable hypodermic syringes.
There are many situations in which after the administration of medication by a hypodermic syringe, the hypodermic syringe should be destroyed because to reuse it may involve the spread of infection. In these circumstances single use disposable syringes are used. However, particularly in third world countries, single use syringes are often reused although they are clearly marked for disposal.
It is an object of the present invention to provide a single use hypodermic syringe which, because of its very construction, is impossible to reuse, after it has been used once.
According to the present invention there is provided a single use disposable hypodermic syringe comprising a hollow cylindrical barrel closed at its front end by a wall, a hypodermic needle mounted in said wall and in fluid communication with the inside of the barrel, an inwardly directed lip means within the barrel extending over at least part of the inner circumference thereof and spaced longitudinally inwardly from the wall to form a pocket therebetween in the barrel, a plunger housed within the barrel and being freely reciprocable therein outside of the pocket, the plunger having piston means of resilient material at the leading end thereof and a plunger rod means extending longitudinally of, within, and beyond, the barrel, and frangible connections between the piston means and the plunger rod means, whereby in operation the plunger on its delivery stroke forces the piston means into the pocket where it is retained by the lip means, any attempt to remove the piston means from the pocket by attempted withdrawal of the plunger, causing the frangible connections to break.
In a preferred form of the invention the piston means has a suction cup means on its leading face and the wall has a co-operating dome member formed on its inner face. Preferably the hypodermic needle, cup means and dome member are positioned eccentrically of the central axis of the syringe.
It is preferred that the frangible connection be immediately behind a flat rear face of the piston means.
According to a feature of the invention the plunger rod has an area of reduced cross section to provide a fracture point and preferably the plunger rod is of cruciform cross section.
Guideways may be provided on the inside of the barrel to engage the plunger rod and prevent its rotation within the barrel. The guideways may extend longitudinally of the barrel near its outer end and for less than half the length of the barrel.
According to a preferred construction the frangible connections comprise a pin on the plunger rod extending transversely of the barrel and received in substantially semi-cylindrical socket arranged transversely at the rear of the piston means. Suitably the piston means may be made of a medical rubber compound and the lip may span the entire inner circumference of the barrel.